Antibody Tests (Coombs Test)

Risks

There is very little chance of a problem from
having blood sample taken from a vein.

You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.

In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.

Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.

Results

Normal

No antibodies are found. This is called a
negative test result.

Direct Coombs test. A negative test result means
that your blood does not have antibodies attached to your red blood
cells.

Indirect Coombs test. A negative test result
means that your blood is compatible with the blood you are to receive by
transfusion. A negative indirect Coombs test for Rh factor (Rh antibody titer)
in a pregnant woman means that she has not developed antibodies against the
Rh-positive blood of her baby. This means that
Rh sensitization has not occurred.

Abnormal

Direct Coombs test. A positive result means your
blood has antibodies that fight against red blood cells. This can be caused by
a transfusion of incompatible blood or may be related to conditions such as
hemolytic anemia
or hemolytic disease of the newborn (HDN).

Indirect Coombs test. A positive test result
means that your blood is incompatible with the donor's blood and you can't
receive blood from that person. If the Rh antibody titer test is positive in a
woman who is pregnant or is planning to become pregnant, it means that she has
antibodies against Rh-positive blood (Rh sensitization). She will be tested
early in pregnancy to check the blood type of her baby. If the baby has
Rh-positive blood, the mother will be watched closely throughout the pregnancy
to prevent problems to the baby's red blood cells. If sensitization has not
occurred, it can be prevented by a shot of
Rh immunoglobulin.